Method and system for regulating the torque-transmission capacity of a frictionally engaged, torque transmitting assembly

ABSTRACT

A method and system for regulating the torque transmitting capacity of a frictionally-engaged torque-transmitting assembly located in the drive train of a motor vehicle. The torque-transmitting assembly has an input and an output, the values of which, such as input torque and output torque, are detected by sensors. The torque values are subjected to a correlation calculation in which a correlation value is calculated. The difference value between the calculated correlation value and a predetermined correlation target value is determined. An adjustment value is determined to reduce the difference value if the difference value exceeds a preset threshold value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a system for regulatingthe torque-transmitting capacity of a frictionally-engagedtorque-transmitting assembly, especially an assembly in the drive trainof a motor vehicle.

2. Description of the Related Art

Assemblies that transmit torque in a frictionally-engaged manner in thedrive train of a vehicle, such as clutches, including converter lockupclutches in the converter of an automatic transmission, transmissionswith endless torque-transmitting means having continuously valuetransmission ratios (CVT transmissions, friction wheel drives),including brakes, are increasingly automated or operated by their ownactuators. The control or the regulation of the frictionally-engagedtransmittable torque of the respective assembly should be as low aspossible for easing the burden of the actuators, as well as for reasonsof low energy consumption and high control or regulation accuracy, butit should be high enough to prevent permanent slippage that can lead torapid wear or to the destruction of the frictionally-engagedtorque-transmitting assembly. Especially because of the latter reason,most of the time an opposite, contact overpressure of thefrictionally-engaged torque-transmitting assemblies results. A contactoverpressure also generally results because wear of components, settlingphenomena, temperature influences, or viscosity-related parameterchanges then do not lead to unintended slippage.

One possibility for detecting the slippage condition of twofrictionally-engaged torque-transmitting assemblies is known from DE 19544 061. To detect the adhesion or sliding limits, apressure-medium-operated actuation element that determines the contactforce of the two frictionally-engaged components, is supplied with anactuation pressure that is superimposed on a modulation signal. Thegradient of the actuation pressure is correlated with a transmissionoutput shaft speed. The actuation pressure is readjusted In accordancewith whether a predetermined correlation value is exceeded or notachieved. It is characteristic of the previously-known method that asensor must be provided for detecting the modulated pressure and thatthe correlation calculation can be more difficult by complex phasedisplacements.

A method for controlling the operation of a frictionally-engagedtorque-transmitting assembly is known from DE 199 59 470 A1, in whichrotational speed fluctuations of an input element and an output elementare correlated with each other without causing the rotational speedfluctuations by modulating the torque-transmitting capacity. Onecharacteristic of that method is that it sweeps a wide frequency rangethat can be a function of the engine rotational speed, for example,which makes a correlation analysis, such as by means of a Fourieranalysis, more difficult.

SUMMARY OF THE INVENTION

The present invention is directed to providing a generic method andsystem for regulating the torque-transmitting capacity of africtionally-engaged torque-transmitting assembly, especially anassembly in the drive train of a motor vehicle, that makes possible in asimple execution the control of an operating condition of africtionally-engaged torque-transmitting assembly in such a way that nounnecessarily high actuation forces are exerted on thefrictionally-engaged components of the assembly.

The goal of the invention is achieved with a method for regulating thetorque-transmitting capacity of a torque-transmitting assembly that isfrictionally-engaged between an input and an output, especially anassembly in the drive train of a motor vehicle, by which method

an adjusting value for influencing the torque-transmitting capacity ismodulated

an output value of the assembly is detected

the output value is subjected to a correlation calculation in which acorrelation value is calculated and

the difference between the calculated correlation value and apredetermined correlation target value is determined and the adjustingvalue is changed in the direction of a reduction of the difference, ifthe difference exceeds a preset threshold value,

an input value and an output value of the assembly are detected and

the correlation value between the input and output values is calculatedin the correlation calculation.

The method In accordance with the invention has the advantage thatalmost no phase shift has to be considered in the correlationcalculation between the two detected values because of the equality ofaction and reaction, which significantly simplifies the evaluation. Inaddition, no special sensor for the measurement of the modulations ofthe control signals is needed. The input and output torques, the inputand output rotational speeds and their deduced values, such aschronological deductions, etc. can be detected or utilized as input oroutput values.

It can be especially advantageous for the method for controlling thetorque transmission capacity of a torque-transmitting assembly that isfrictionally-engaged between an input and an output, especially anassembly in the drive train of a motor vehicle, to impress a modulationsignal on an input value for monitoring the quality or quantity of thetorque transmitted, for example a pressure signal for pressurizing aendless torque-transmitting means to a conical disk set, whereby atleast two measurement values are detected as signal responses betweenthe impression of the modulation signal and the output of the assemblyand the at least two measurement values are correlated with each other.The resulting correction value is utilized for the correction of theinput value. The measurement values can, for example, be a measurementvalue provided by a pressure sensor and that can be appropriatelyprepared and filtered, and/or it could be a slippage component that canbe formed, for example, by the rotational speed difference between aninput shaft and the output shaft of a CVT transmission whereby, ifnecessary, a change occurring in the transmission ratio during thedetermination of the measurement value needs to be considered. In thatway a measurement value can be utilized as a reference value that isdirectly deduced from the control circuit by evaluating two informationsources of the assembly. Especially if there is a phase relationshipbetween one measurement value and the modulation signal with atime-delayed signal response, an improvement in the correlation valuecan be achieved in contrast to a reference signal that is deduceddirectly from the signal generator that issues the modulation signal.

In accordance with another inventive aspect, by the detection of theinput rotational speed and the output rotational speed of an assemblythere is the accompanying advantage that no special sensors are requiredbecause the appropriate rotational speed sensors are already generallypresent.

The invention is also directed to a system for regulating thetorque-transmitting capacity of a frictionally-engagedtorque-transmitting assembly, especially an assembly in the drive trainof a motor vehicle, that includes a control device for setting anadjusting value that determines the torque-transmitting capacity of theassembly, a modulation device for modulating the adjusting value, asensor for detecting an input value of the assembly, a sensor fordetecting an output value of the assembly, and an electronic controldevice with a processor and a storage unit that is constructed in such away that it carries out the inventive method.

The torque-transmitting assembly, as mentioned above, can be ofdifferent types. The invention can be utilized advantageously with acontinuously variable transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description based uponschematic drawings as examples and with additional details.

There is shown in the drawings:

FIG. 1 a diagram of a motor vehicle with a drive train,

FIG. 2 a section through a CVT transmission with an input-side clutchand an output,

FIG. 3 a hydraulic diagram for controlling a CVT transmission,

FIG. 4 a further hydraulic diagram for controlling a CVT transmission,

FIG. 5 a flow diagram of a control algorithm, and

FIGS. 6 a to 6 e time functions of various signals utilized in carryingout the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with FIG. 1 a motor vehicle has an engine 2 that isconnected by way of a clutch 4 and a transmission 6 with a propellershaft 8. By way of a differential 10 the propeller shaft drives driveshafts 12 that are non-rotatably connected with the rear wheels 14. Thefront wheels 16 in the illustrated example are not driven.

An electronic control unit 18 including in a known way a microprocessorwith accompanying storage units has inputs 20 that are connected withsensors. As sensors there are provided, for example, a sensor 22 fordetermining the rotational speed of a transmission input shaft, athrottle-valve sensor 24, an engine rotational speed sensor 26, apropeller shaft rotational speed sensor 28, and, if necessary,additional sensors.

Outputs of the control unit 18 are connected with a clutch actuationdevice 32 and a transmission actuation device 34, as well as, ifnecessary with other actuators of the drive train, such as a throttleactuator, and the like.

Transmission 6 in the illustrated example is a CVT transmission, whoseactuation unit 34 is controlled hydraulically.

FIG. 2 schematically shows important components of the clutch and thetransmission of FIG. 1. An input shaft 36 that is non-rotatablyconnected with the crankshaft of the engine drives, by way of clutch 4and the reversing set 38, a first conical disk pair 40 of CVTtransmission 6. The first conical disk pair 40 is connected with asecond conical disk pair 42 by way of an endless torque-transmittingmeans 44. The endless torque-transmitting means 44 is in frictionalengagement with each of the conical disk pairs 40 and 42. Through anoutput shaft 46 the second conical disk pair 42 drives the differentialabutting the transmission in the example of FIG. 2, which in theillustrated example drives the front wheels.

A hydraulic system 48 that is supplied with pressure by a pump 50 servesto control the clutch and the transmission.

The contact pressure of the conical disks against the endlesstorque-transmitting means results hydraulically, but it can occurdifferently, for example, by way of an electric motor, a spring,centrifugal force, and the like. It is important that at least one partof the contact pressure is freely controllable by an actuator. Twodesign variants of a hydraulic contact pressure control are shown inFIGS. 3 and 4.

In accordance with FIG. 3, a valve A controls the pressure that isapplied to the second conical disk pair 42. A valve B controls thepressure that is applied to the first conical disk pair 40. Thereby, thecontact pressure can be controlled with the valve A, while thetransmission ratio adjustment takes place together with the valve B.Valve A is freely controllable, for example by an electromagneticcontrol that is controlled by way of appropriate logic circuits.

In the embodiment In accordance with FIG. 4, the contact pressure iscontrolled by a combination of a valve C with a hydraulic mechanicaltorque sensor 52. The valve C is freely controllable; the torque sensor52 controls the pressure as a function of the applied torque. Thereby,one part of the contact pressure is freely controllable and a furtherpart as a function of the torque. The adjustment of the conical diskpairs takes place as a result of a differential pressure between theconical disks 40 and 42 by way of a valve D.

Measurement values for the transmission control are, for example, theoutput signal of the throttle-valve sensor 24 or other measurement orcontrol values with which the output torque of the engine can beestimated.

The components and their arrangements described so far are known as suchand will therefore not be explained more precisely with regard to theirconstruction or function.

The contact pressure controlled by valve A of FIG. 3 and of valve C ofFIG. 4, with which the conical disk pairs lie against the endlesstorque-transmitting means 44, should be so low that slippage between theendless torque-transmitting means 44 and the conical disk pairs isavoided, and is not unnecessarily high. The contact pressure is normallypilot controlled by a characteristic field stored in control device 18.It can be fine-tuned or controlled in accordance with other operatingparameters.

FIG. 5 shows a flow diagram of a method in accordance with which valve Aof FIG. 3 or valve C of FIG. 4 can also additionally be suitablyactuated in order to correct faulty pilot control values of the valvepositions stored in control device 18.

If the control device determines an appropriate actuation time window 50that is, for example a function of certain operating parameters of theentire drive train, valve A or valve C can be modulated by a modulatorin step 52, for example by an adjustment value determined by an electricmotor, whereby the modulation amplitude is small compared with theadjustability of the valve or the appropriate adjusting value.

The transmission input rotational speed is detected in step 54 by thesensor 22; at the same time the propeller shaft rotational speed isdetected in step 56 by sensor 28, which can be converted with the helpof the known transmission ratio of the transmission directly into thetransmission output rotational speed. It is advantageous if sensor 28 isnot located on the propeller shaft but detects the rotational speed ofthe transmission output shaft directly, similar to sensor 22, as themeasurement results will not be falsified by deflections and swingingmasses between the output shaft of the transmission and the propellershaft.

The input rotational speeds and the output rotational speeds over thecourse of time as measured during the activation time window, whichspeeds are stored in a suitable memory of control unit 18, are filtered,for example subjected to low-pass, band-pass, and high-pass filtering infiltering steps 58 and 60, in order then to be forwarded to acorrelation calculation in step 62, in which the correlation between thefiltered signal patterns is determined. After further filtering in step64, the calculated correlation value is forwarded to a controller instep 66 in which the calculated correlation value is compared with thecorrelation target value 67 stored in control unit 18. In step 66 acorrection value that corresponds with the variation between thecorrelation target value and the calculated actual correlation value isgenerated by the controller and leads in step 68 to a change of theposition of the valve that controls the contact pressure between theconical disks.

As shown in FIG. 5, the method in accordance with the invention can runcontinuously, so that another cycle can be carried out after anadjustment of the actuator for the control valve.

The modulator utilized in step 52 can be in continuous operation and theslow, timewise change of the adjusting value that determines theposition of the valve can be superimposed on a modulation fluctuation.Alternatively, the modulation and appropriately the method in accordancewith the invention can occur only in predetermined time windows, inwhich an especially accurate control of the valve or the contactpressure of the conical disks results.

The adjustment of the valve based upon the evaluation of the correlationvalue can take place incrementally which means independently of thevalue of the deviation between the correlation value and the correlationtarget value, which can be performed until the deviation falls below athreshold value. The control can also take place proportionally or inaccordance with other strategies.

The method in accordance with the invention can be changed in variousways. For example, instead of the input rotational speed and the outputrotational speed the input torque and the output torque of thetransmission can be determined and utilized for a correlationcalculation similar to the method explained in FIG. 5. The determinationof the rotational speeds has the advantage, moreover, that it can bedone with available sensors. Instead of determining the rotationalspeeds or the torques, their changes over time could be determined orcalculated and taken as the basis for the correlation calculation.

All suitable algorithms with which time-based relations between twomeasured values can be quantified can be introduced for the correlationcalculation.

The correlation target value that is stored in control unit 18 can bedynamic, meaning it can depend on the operating parameters of the entiredrive train, for example, whether driving on slippery ground where thedrive train should be protected from torque fluctuations undercircumstances caused by possibly suddenly slipping wheels, that is, theslippage of the transmission and therewith the contact pressure can bereduced, etc. The method In accordance with the invention can also beutilized with appropriate sensor placements for the control of theclutch or other devices that transmit torque in a frictionally-engagedmanner, for example also a brake.

In accordance with the invention, the following actuation mechanisms canbe utilized, for example:

An engine actuation: The engine is utilized as an actuation source basedon its irregular movements.

A modulation of the transmitting capacity: The performance-transmittingcomponent, such as, for example, a clutch or a conical disk set of atransmission, has an adjustment value with which the transmittingcapacity can be influenced (e.g., contact pressure). If a periodicfunction is superimposed on the adjustment value signal, thetransmitting capacity can be modulated.

An irregularly geared input step: Based upon an irregularly-operatinginput step, a rotational speed/rotational speed modulation can likewisebe created. The actuation frequency is a function of the rotationalspeeds.

In accordance with the invention the following values can be utilized assignals:

Input rotational speed (or derived values, such as rotationalacceleration);

Output rotational speed (or derived values, such as rotationalacceleration);

Input torque;

Output torque;

Adjustment values for the modulation of the transmitting capacity;

Difference between the input and output rotational speeds; and

Ratio of the input rotational speed to the output rotational speed

The signals can be subjected to a filter routine, (for example, highpass, band pass, low pass) or any other process before furtherprocessing.

In accordance with the invention the following evaluation methods can beutilized:

Cross-correlation between each of two differing signals. Thecross-correlation can be normalized or not normalized. Likewise, themaximum or minimum occurring correlation coefficient for different shifttimes can also be selected.

Fourier transformation for each of the above-identified signals.

Filtration of one of the above-named signals.

Lock-in method (between two different signals; the method is explainedbriefly below).

Combinations of actuation mechanisms, signals, and evaluation methodsare also suitable for slippage determination in accordance with theinvention. The change of the transmitting capacity can be utilized, forexample, as a means of modulation. The rotational speed difference andthe adjustment value of the modulation can serve, for example, as anevaluation signal. The slippage can be determined with the method inaccordance with the lock-in principle.

Reference should be made to FIGS. 6 a to 6 e for details of the lock-inprinciple. The lock-in process is a method for detecting a signal thatis weaker than noise or interference signals.

The operation of the lock-in is schematically shown in FIGS. 6 a to 6 e.In FIG. 6 a, a signal A is shown as a function of time. Signal A is, forexample, the measured contact pressure signal of a transmission. In FIG.6 b, a signal B is shown as a function of time. Signal B is the resultof the measurements of the rotational speeds of a first conical disk setand a second conical disk set and a subsequent differential form of therotational speeds.

A signal C is shown as a function of time in FIG. 6 c. Signal C isderived from reference signal A. That signal only assumes values between−1 and 1 and contains the correct “cycle” of the contact pressurereference signal. If signal C is multiplied by signal B, the amplitudesof the differential rotational speeds are “lapped” upwards, see FIG. 6 dwith signal D. If one subsequently applies a low pass filter to signalD, the result is an average amplitude, as can be seen from signal E, seeFIG. 6 e. The amplitude of signal E is proportional to the slippage ofthe variable speed unit or of the system of the clutch or thetransmission.

The claims included in the application are illustrative and are withoutprejudice to acquiring wider patent protection. The applicant reservesthe right to claim additional combinations of features disclosed in thespecification and/or drawings.

The references contained in the dependent claims point to furtherdevelopments of the object of the main claim by means of the features ofthe particular claim; they are not to be construed as renunciation toindependent, objective protection for the combinations of features ofthe related dependent claims.

Although the subject matter of the dependent claims can constituteseparate and independent inventions in the light of the state of the arton the priority date, the applicants reserve the right to make them thesubject of independent claims or separate statements. They can,moreover, also embody independent inventions that can be produced fromthe independent developments of the subject matter of the includeddependent claims.

The exemplary embodiments are not to be considered to be limitations ofthe invention. On the contrary, many changes and variations are possiblewithin the scope of the invention in the existing disclosure, inparticular such variants, elements, and combinations and/or materialswhich, for example, are inventive by combining or modifying singlefeatures that are in combination and are described individually inrelation to the general specification and embodiments as well as theclaims and shown in the drawings, as well as elements or method stepsthat can be derived by a person skilled in the art in the light of thedisclosed solutions of the problem, and which by means of combinedfeatures lead to a new object or new method steps or sequences of methodsteps, as well as manufacturing, testing and operational procedures.

1. A method for regulating the torque-transmitting capacity of atorque-transmitting assembly in the drive train of a motor vehicle andthat is frictionally engaged between an input and an output, said methodcomprising the steps of: detecting an input value parameter and anoutput value parameter of the assembly, providing an adjustment valuethat influences the torque-transmitting capacity of the assembly,modulating by the adjustment value an operating parameter of theassembly that influences the torque-transmitting capacity, subjectingthe detected input and output values to a correlation calculation inwhich a correlation value between the input and output values iscalculated, determining the difference between the calculatedcorrelation value and a predetermined target correlation value and,changing the adjustment value in the direction of a reduction of thecorrelation value difference when the difference exceeds apre-determined threshold value.
 2. A method in accordance with claim 1,wherein the input and output values are detected during the same timeinterval during which the adjustment value is modulated.
 3. A method inaccordance with claim 1, including the step of filtering the detectedvalues before the correlation calculation.
 4. A method in accordancewith claim 1, wherein at least one of the target correlation value and adifference threshold value are functions of the operational parametersof a drive train included in the assembly.
 5. A method in accordancewith claim 1, including the step of detecting the input rotational speedand the output rotational speed of the torque-transmitting assembly. 6.A system for regulating the torque-transmitting capacity of africtionally-engaged torque-transmitting assembly, in the drive train ofa motor vehicle, said system comprising; a control unit for setting anadjustment value that determines the torque-transmitting capacity of theassembly, a modulation unit for modulating the adjustment value, asensor for detecting an input parameter value of the assembly, a sensorfor detecting an output parameter value of the assembly, and anelectronic control unit including a processor and a storage unit forregulating the toque-transmitting capacity of the assembly.
 7. A systemin accordance with claim 6, whereby the torque-transmitting assembly isa steplessly adjustable, continuously variable transmission.
 8. A methodfor regulating the torque-transmitting capacity of a torque-transmittingassembly in the drive train of a motor vehicle and that is frictionallyengaged between an input and an output, said method comprising the stepsof: impressing upon an operating parameter modulation signal associatedwith the assembly an adjustment value for influencing thetorque-transmitting capacity of the assembly, detecting at least twomeasured value signals representing operating values of the assemblybetween the output and the impression of the modulation signal,processing the at least two measured value signals, subjecting the atleast two measured values to a correlation calculation in which acorrelation value is calculated, and utilizing the correlation value forcorrecting the adjustment value.